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Asynchrony During
Mechanical VentilationKaren J. Bosma, MD, FRCPC
Disclosure Statement• I have received research funding from
Covidien to support a clinical research
assistant
October 30, 2012
Objectives•To define patient-ventilator asynchrony
•To understand why it occurs
•To recognize major types of asynchrony
•To learn ways to manage asynchrony
Syn∙chro∙nySimultaneous occurrence of events
Critical Care Western
A∙syn∙chro∙nyEvents not coordinated in time
Assisted Spontaneous BreathingPvent + Pmus = (Flow * Resistance) + (Volume * Elastance)
Definition
• Patient-Ventilator Asynchrony occurs when the
timing of the ventilator cycle is not simultaneous
with the timing of the patient’s respiratory cycle
• Neural Ti ≠ Ventilator Ti
• Neural Te ≠ Ventilator Te
Associated with Weaning Failure
Patients with high level of asynchrony:
– Longer duration of MV
– Higher incidence of tracheostomy
– Less likely to successfully wean from MV
– Longer ICU LOS
– Longer Hospital LOS
– Less likely to be discharged home
Thille, Intensive Care Med (2006) 32:1515-22, Chao, CHEST (1997) 112:1592-99
De Wit, Critical Care Medicine (2009) 37: 2740-45
Assisted Spontaneous Breathing
Patient-ventilator
interaction:
-Mechanical properties
of lung and chest wall
-Neural function
-Clinical input
Key Phases of Each Breath
Jolliet and Tassaux, Crit Care (2006) 10:236-42
•Trigger
sensitivity
•(PEEPi)
•Initial
flow rate
•Set pressure
•Control of flow
•(responsiveness to
patient demand)
•Set Ti
•% of peak flow
•(elastance and
resistance)
Case 1
Asynchrony During Mechanical Ventilation
Case 1
• Mr. H., 63 year old male with emphysema admitted to ICU with COPD exacerbation
• Current active issue: Prolonged weaning from mechanical ventilation.
Case 1 continued
• Progress: Remains on PSV 16-18 cmH2O ; at every attempt to reduce PSV below 15 cmH2O, RR 40, and is therefore placed on higher PSV at which RR 18-22. The airway pressure and flow tracings seen on the ventilator are shown below.
PSV 16 (Paw (cmH2O) top and Flow (L/sec) bottom)
PSV 12 (Paw (cmH2O) top and Flow (L/sec) bottom
PSV 16 (Paw (cmH2O) top and Flow (L/sec) bottom)
PSV 12 (Paw (cmH2O) top and Flow (L/sec) bottom
Ineffective Efforts
Flow
Pao
Peso
Ineffective Efforts (IE) Patient 1 Ventilator 0
COPD ( Auto-PEEP )
Measures to Reduce PEEPi
• Reduce resistance in airways
• Bronchodilators and steroids
• Tube patency – remove secretions
• Prolong expiratory time
• Reduce inspiratory time (cycle sooner)
• Decrease respiratory rate
• Decrease Tidal Volume
• Decrease pressure support
PSV 16 (Paw (cmH2O) top and Flow (L/sec) bottom)
PSV 12 (Paw (cmH2O) top and Flow (L/sec) bottom
Flow
Pao
Peso
Mechanical Ti > Neural Ti
Delayed Cycling (DC) Patient 2 Ventilator 1
Delayed Cycling
Delayed Cycling
Delayed Cycling
Delayed Cycling
PSV 16 (Paw (cmH2O) top and Flow (L/sec) bottom)
PSV 12 (Paw (cmH2O) top and Flow (L/sec) bottom
Adverse effects of bothinsufficient and excessive levels
of pressure support
Goal: provide optimal unloading of the respiratory muscles
Case 2
Asynchrony During Mechanical Ventilation
Case 2
• A 24 year old woman is admitted with ARDS
• 10 days later the patient is improving.
• FiO2 has been weaned to 0.40 and PEEP is at 10 cmH2O
• CXR, although improved, still shows bilateral airspace disease
• You would like to start weaning the patient from the ventilator and order sedation to be weaned.
• However, when sedation is lightened, the patient “does not tolerate pressure support” and looks asynchronous on assist control.
Case 2 continued
• Flow (L/sec) (top) and Airway Pressure (cmH2O) (bottom) shown below:
Double Triggering
Flow
Pao
Peso
Mechanical Ti < Neural Ti
Double Triggering (DT) Patient 1 Ventilator 2
Premature Cycling
25%
10%
Cycle
setting
Neural Ti
Measures to Reduce
Double Triggering
• Double triggering occurs in setting of high
ventilatory demand and short ventilator
inspiratory time (ACV more common than PSV)
• Aim for ways to reduce ventilatory demand
– Increase Vt
– Sedation
• Increase Ti
– Reduce cycling criterion (Esens), or increase Ti
Case 3
Asynchrony During Mechanical Ventilation
Case 3
• An 80 year old woman, admitted to ICU with pneumonia, dehydration and weight loss.
• PMHx: congestive heart failure• The nurse calls you to the bedside. The ventilator
keeps alarming for “high respiratory rate.” The patient’s respiratory rate is 35 to 40.
• The RRT has tried assist control/ pressure control, assist control/volume control and pressure support, but “cannot get the patient to settle.”
• The nurse would like an order for more sedation and asks if you are considering paralyzing the patient.
Case 3 continued• The patient is awake, with a high respiratory rate, but
no other signs of distress. • The airway pressure (bottom) and flow tracings (top)
seen on the ventilator are shown below.
Auto-triggering
Flow
Pao
Peso
Autotriggering (AT) Patient 0 Ventilator 1
Auto-triggering
• The delivery of a mechanical breath in the absence of a clear contraction of the respiratory muscles.
Auto-triggering
• Circuit leak
• Water in the circuit
• Cardiac oscillations
• Nebulizer treatments
• Negative suction applied through chest tube
• Fix leak, empty water from circuit
• Increase Trigger sensitivity
• Change from flow to pressure triggering
Case 3 continued
• You increase the trigger threshold (make it less sensitive) and the RR immediately drops to 24, and the patient, appearing more comfortable, drifts off to sleep. However, soon the nurse is calls to let you know that now the ventilator is alarming for apnea. Although the patient is on fentanyl at 50 ug/hr, she arouses easily and obeys commands.
ABG: pO2 89, pCO2 30, pH 7.50, HCO3- 24
Periodic Breathing
Flow
Pao
Peso
10 seconds
Central apnea
Summary
Asynchrony During Mechanical Ventilation
Types of Gross Asynchrony
Patient Breath
Ventilator Breath
Triggering Problem
Ineffective Efforts (IE) 1 0
Autotriggering (AT) 0 1
Cycling off Problem
Double Triggering (DT) 1 2
Delayed Cycling (DC) 2 1
Bedside Management
Respir Care. 2011;56(1):61–72.
Type Correction
Ineffective triggering–weak inspiratory effort–High PEEPi (COPD)
Decrease trigger thresholdReduce sedationReduce the potential for intrinsic PEEP (decrease VT, VE, increase TE)
Delayed Cycling-Low elastic recoil (emphysema) -High resistance (COPD)
Increase cycling criterion (Esens)Decrease Ti
Auto-triggering–cardiogenic oscillations or circuit leaks–absence of patient effort
Increase trigger thresholdSwitch from flow to pressure triggeringAvoid hyperventilation
Double-triggering-high ventilatory demand, and-short ventilator inspiratory time (ACV more common than PSV)
Aim for ways to reduce ventilatorydemand.Is VT too small? TI too short? Decrease cycling criterion (Esensitivity)
Assisted Spontaneous Breathing
Patient-ventilator
interaction:
-Mechanical properties
of lung and chest wall
-Neural function
-Diaphragm contraction
-Clinical input
PAV
Flow
Pao
Peso
Pmus = Flow*Rtot + Vt*Est
PAV instantaneously
measures the flow and
volume being pulled in by
the patient, and, knowing the
elastance and resistance of
the respiratory system,
determines how much
pressure to provide for each
breath.
NAVA
Future
Research
Asynchrony During Mechanical Ventilation
Asynchrony
may be costly
Critical Care Western
Reducing patient-ventilator asynchrony may improve outcome
IF
THEN
↓ Delirium
↓ Duration MV
↓ ICU LOS
↓ Hospital LOS↓ Mortality
↓ Asynchrony
↑ Sleep Quality
?↓ Sedation
? ↓ VIDD
↓ Asynchrony
Key issues of patient-ventilator interaction during
Variable Gas Flow Delivery (PSV)
Delays in Flow Delivery
Active Exhalation Initiating Cycling
Neurally Adjusted Ventilatory Assist